Glenn,
The factory uses a "points" system to determine the correct spring mount to be used for your car. Your vehicles options are rated on a point scale and the total determines the mount to be used. There are also "tabs" located on the mounts that can be used to determine what to use. If you use anything other than what your car was built with, it will affect your alignment (raising or lowering your car).
I would personally use Bilstein shocks, either comfort or heavy duty unless your car is equipped with the Sportline package.

I have done exactly what you are contemplating to my very own '91 300E. Alot of work but well worth it. be sure and load the suspension before tightening the rear suspension pieces.